Tobacco use is the leading preventable cause of mortality in the United States. Although the majority of smokers want to quit, most quit attempts are unsuccessful. Research suggests that partner support is critical to smoking cessation, but studies manipulating the provision of support do not improve quit rates. It is possible that studie examining perceived support behaviors at only one time point from only one partner do not capture the actual proximal partner behaviors that influence relapse and abstinence. The objective of the current application is to understand how real-time partner behaviors affect smoking. The central hypothesis is that the behavior of one partner can affect the smoking/quitting behaviors of the other partner indirectly, through their influence on the smoker's self-control. The rationale for this project is that identifying the partner behaviors tha influence smoking will provide the knowledge needed to strengthen behavioral interventions for smoking cessation. The central hypothesis will be tested by pursuing two specific aims: 1) identify positive and negative partner behaviors proximally associated with smoking, and 2) identify individual differences that moderate proximal influences on smoking outcomes. Under the first aim, ecological momentary assessment (EMA) will be used to examine the effect of partner behaviors on the smoker's momentary self-control and subsequent smoking outcomes. It is expected that positive partner behaviors (unrelated to smoking) will be associated with greater self-control strength in the smoker and better subsequent smoking outcomes. Conversely, negative partner behaviors (unrelated to smoking) will be associated with lower self-control strength and poorer subsequent smoking outcomes. Under the second aim, individual differences measured at baseline will be tested as moderators of these effects. It is expected that the association between positive partner behavior and improved smoking outcomes will be stronger for smokers with high than with low relationship quality. It is also expected that the association between negative partner behaviors and poorer smoking outcomes will be stronger for smokers with high impulsivity than with low impulsivity. Finally, it s expected that the association between self-control strength and smoking outcomes will be stronger for participants low in motivation to quit or high in nicotine dependence. The proposed research is theoretically innovative because it departs from prior research in arguing that partner behaviors unrelated to the quit attempt are the most important for smoking cessation. The proposed research is methodologically innovative because it involves studying both smoker and partner behaviors proximally through EMA during a smoker's quit attempt, rather than through one person's self-reported assessments at baseline or at follow-up. The proposed research is significant because it is a first step in determining which partner behaviors are in fact consequential for the actor's smoking cessation. Ultimately, such knowledge has the potential to inform enhanced behavioral and social interventions that include changes in partner behavior as a component of smoking cessation.